Easiest way to show ads in a native app on iOS... oh wouldn't that be iAd service in which Apple gets a cut of the profit?
The WWDC session for this feature specifically highlights a major privacy issue this can help solve: blocking privacy-invading tracking scripts.
It's completely possible to show ads without tracking every move the user makes across the web.
What i think is that by making it harder to put ads in mobile web content, they'll make it more expensive as well, and thus push toward higher quality ad networks ( better targeting, better speed, better content).
Just like the end of flash saw an increase of quality SPA HTML5 frameworks.
As a real world example, the (otherwise excellent) Twitch app on iOs serves unskippable minute long video ads with an annoying frequency, so much that I often prefer using the service through an ad-blocking web browser (which btw DO exist on the App Store, and have been for a while already).
(I'm not endorsing this point of view myself, although it sounds more than a bit plausible to me; it's just, I think, what was being said.)